A switching device of this generic type has been available on the electrical equipment market for many years. In such switching devices or protective devices, an arc occurs at the opening contact points when electric currents are being disconnected. This arc causes wear at the contact points due to the contact material burning away, and delays the disconnection of the circuit, since the current continues to flow via the arc until the arc is extinguished. In order to limit the damage caused by the arc, electrical switching devices or protective devices beyond a certain rating are equipped with an arc extinguishing device.
Such an arc extinguishing device often comprises, as shown in FIG. 4, an arcing chamber 1 with arc runner plates 2 and 3, and various components which, inter alia, also carry out tasks relating to flow.
According to FIG. 5, the arcing chamber 1 is designed as a pack of arc splitter plates 4, which are stamped in a U-shape, are arranged parallel and are held at a distance from one another. A strip of insulating material, generally a vulcanized fiber strip 5, is folded around the arc splitter plates 4, keeps the arc splitter plates 4 at a distance from one another, and forms an assembly. Openings 6 are stamped in the insulating strip 5 and, inter alia, influence the flow behavior in the arcing chamber 1. The runner plates 2 and 3 are arranged at the upper end and at the lower end of the arcing chamber 1, according to FIG. 4. Together with a moving contact link 7, the upper arc runner plate 2 forms a contact point 8.
FIG. 6 shows a cross-section illustration of the arc extinguishing device to show how the arc moves from the contact point into the arcing chamber. When the contact point 8 opens, an arc 9 is formed between the contacts as they move away from one another. Electromagnetic forces move the arc 9 in the direction of the arc extinguishing chamber 1. The roots of the arc 9 at the outlet points of the arc runner plates 2 and 3 in this case move away from the contact point 8 along the arc runner plates 2 and 3, which are electrically connected to the circuit. The arc runner plates 2 and 3 are in this case formed and arranged such that they lead the arc to the arcing chamber 1 as quickly as possible. The arc 9 is then extinguished in the inner part of the arcing chamber 1. During the described sequence, electromechanical and thermomechanical forces occur between the arc splitter plates 4 and the arc runner plates 2 and 3. If the arc runner plates 2 and 3 are not fixed to be sufficiently robust--and it is often the case that they are not adequately fixed owing to the design characteristics--they touch the outer arc splitter plates 4, and are welded to them. This reduces the efficiency of the arcing chamber 1 for further extinguishing processes. In the case of particularly severe arcs, such as those which occur as a consequence of short-circuit disconnections, there is a risk of these arcs running through the arcing chamber and being short-circuited behind it. In this case, the arcing chamber no longer has any extinguishing effect.
The following solutions are already known to prevent the arc from being short-circuited in the space located behind the arcing chamber. The arc runner plates are kept relatively short, that is to say they do not continue to the end of the arcing chamber, where the arc splitter plates end. Another option is to dispense with the lower arc runner plate entirely. Normally, the arc runner plates that are kept very short are either not mechanically supported at all, or else an additional plastic part is used for support, although this involves corresponding additional costs. The solution with short runner plates has the major disadvantage that, in some circumstances, the entire volume of the inner part of the arcing chamber is not used optimally during the extinguishing process.